1. Field of the Invention
The present invention relates to an improvement of signal processing in information recording/reproduction using an information medium such as an optical disk. In particular, this invention relates to a method of evaluating a signal quality in information recording/reproduction, an improvement of an information recording/reproducing system, and an improvement of a recording compensation method.
2. Description of the Related Art
Jpn. Pat. Appln. KOKAI Publication No. 2000-90436 describes a prior-art information recording system using an optical disk. In brief, in this system, information recorded on an optical disk is reproduced as a weak analog signal using a PUH (pick-up head). The reproduced analog signal is amplified by a pre-amplifier to have a sufficiently high signal level, and then the resultant signal is converted by a level slicer to a binary signal corresponding to a mark/space.
On the other hand, a channel clock signal that is phase-synchronized with the binary signal is generated from a PLL (phase lock loop) circuit. Based on the binary signal and the channel clock signal, parameter calculation means calculates a waveform correction amount. Further, based on the waveform correction amount, record data and a reference clock signal, record waveform generating means generates record waveform pulses. A laser beam corresponding to the record waveform pulses is radiated on the optical disk from the PUH, and information corresponding to the record data is recorded on the optical disk as marks/spaces.
In the above prior art, the waveform compensation amount is calculated from the phase difference between the rising edge or falling edge of the binary signal and the channel clock signal. This technique is effective when the slicing method is adopted for discriminating the content of the reproduction signal. However, this technique is not applicable to the case of, e.g. an integral detection method wherein the reproduction signal is discriminated based on the amplitude value of a reproduction signal sample. In particular, where the recording density is high as in the case of an optical disk system using a blue light laser, the use of the slicing method as the discrimination method is inadequate, and a high-level discrimination method such as a PRML (Partial Response and Maximum Likelihood) method is required. In the PRML method, too, the reproduction signal content is discriminated based on the amplitude value of the reproduction signal sample, and thus the above-described prior art is inapplicable. In short, the reproduction signal quality cannot properly be evaluated or a proper waveform correction amount cannot be calculated in the technique wherein the reproduction signal is discriminated on the basis of the amplitude value of the reproduction signal sample.